This application is based on an application No. 2001-158902 filed in Japan, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a novel water treatment system which is capable of sterilizing water contained in various types of water containers ranging from large-scale water containers such as swimming pools and bathing pools in bathhouses to medium-scale water containers such as water supply tanks on building rooftops and small-scale water containers such as bathtubs for general domestic use.
2. Description of Related Art
To maintain the quality of water in indoor and outdoor swimming pools, for example, the water is periodically sterilized by adding so-called chlorinated lime (bleaching powder or high-concentration bleaching powder) or an aqueous solution of sodium hypochlorite (NaClO) to the water in the pools.
Conventionally, the sterilizing operation is manually performed by pool workers. In addition, the chlorinated lime and the sodium hypochlorite aqueous solution are irritating, so that the sterilizing operation should be performed after business hours. Thus, greater efforts are required for the sterilizing operation.
Furthermore, the chlorinated lime is in a solid powdery form, so that it takes some time for homogeneous dissolution of the chlorinated lime after the addition thereof. During this period, the swimming pool is not available.
The inventor of the present invention previously invented a water treatment system which has a water treatment line for introducing to-be-sterilized water into an electrolysis chamber from a water container, sterilizing the water by way of an electrochemical reaction, and feeding the water back into the water container.
In the water treatment system according to the preceding invention, the to-be-sterilized water is supplied into the electrolysis chamber having electrodes, and subjected to the electrochemical reaction (so-called electrolysis). At this time, chlorine gas, hypochlorous acid (HClO) and hypochlorite ions are generated by the electrochemical reaction, and dissolved in the water for the sterilization of the water.
In the case of the swimming pool, however, the water quality tends to significantly vary depending on the number of swimmers, weather and atmospheric temperature. Where the number of swimmers sharply increases to result in rapid deterioration of the water quality, for example, the electrolysis in the electrolysis chamber alone does not suffice for the sterilization. In this case, the sterilization operation is performed by manually adding an agent to the water as well as by performing the electrolysis. This results not only in an increase in burden on the workers but also in unstable water quality.
The present invention is intended to solve the aforesaid problems, and it is therefore an object of the invention to provide a novel water treatment system which is capable of easily and efficiently performing a sterilization operation to properly maintain the water quality.
In accordance with the present invention, there is provided a water treatment system for sterilizing water retained in a water container, the system comprising: a circulation process line for pumping the to-be-sterilized water out of the water container, sterilizing the water through electrolysis, and feeding the sterilized water back into the water container; means for producing a sterilizing solution having a sterilizing function by electrolyzing an electrolytic solution containing chlorine ions and having a function of promoting an electrochemical reaction; and means for supplying the produced sterilizing solution into the circulation process line as required.
The system can constantly sterilize the water in the circulation process line and, as required, additionally supply the sterilizing solution produced by the sterilizing solution producing means into the circulation process line according to a variation in the quality of the water. Thus, the quality of the water in the water container can properly be maintained.
The sterilizing solution preliminarily produced through the electrolysis of the electrolytic solution by energizing the electrode set in the first electrolysis chamber is stored and, as required, supplied into the water container according to the quality of the to-be-sterilized water. Thus, the amount of the sterilizing solution to be added to the water can promptly be changed according to the quality of the water which varies depending on the number of swimmers, weather and atmospheric temperature. Therefore, where the concentration of the residual chlorine is expected to be reduced by a steep increase in the number of swimmers during business hours of a swimming pool, or by rises in atmospheric temperature and water temperature due to a change in weather, the residual chlorine concentration can be restored as soon as possible to virtually stabilize the water quality. Where the sterilizing solution is not required so much with a smaller number of swimmers, the sterilizing solution preliminarily produced in the first electrolysis chamber is stored so as to be ready to cope with a sudden reduction in the residual chlorine concentration. As a result, the water quality can be adjusted with a sufficient margin of the sterilizing capacity even if the number of swimmers steeply increases.
Since the concentration of the sterilizing solution produced in the electrolysis chamber can be adjusted to a predetermined level by the concentration adjusting means, the treatment capacity of the system can be controlled as desired to increase the efficiency of the electrochemical reaction caused by the electrode set or to adjust the concentration of the sterilizing solution according to the water quality which varies depending on the number of swimmers, the weather, the ambient temperature and the like.
The control of the concentration of the sterilizing solution can be achieved by adjusting the concentration of the electrolytic solution retained in the first electrolysis chamber. That is, the concentration of the sterilizing solution produced by the energization of the electrode set is proportional to the concentration of the electrolytic solution (e.g., salt water) electrolyzed by the electrode set. FIG. 1 is a graph in which an electrolysis period (mm) is plotted as abscissa and a residual chlorine concentration (ppm) of the sterilizing solution produced by the electrolysis is plotted as ordinate. In this graph, there are shown the results of the electrolysis of three kinds of salt water respectively having NaCl concentrations of 1%, 2% and 3%. In the case of the salt water having an NaCl concentration of 1%, the residual chlorine concentration increases with the electrolysis period until the electrolysis period reaches 150 minutes, and is then saturated. In the case of the salt water having an NaCl concentration of 2%, the residual chlorine concentration increases with the electrolysis period until the electrolysis period reaches 180 minutes, and is then saturated. In the case of the salt water having an NaCl concentration of 3%, the residual chlorine concentration increases with the electrolysis period until the electrolysis period reaches 220 minutes, and is then saturated.
Thus, the residual chlorine concentration or the concentration of the sterilizing solution increases with the electrolysis period to a predetermined level corresponding to the concentration of the electrolytic solution retained in the first electrolysis chamber, and is then saturated.
Therefore, the concentration of the sterilizing solution produced through the electrolysis by the electrode set can be controlled by adjusting the concentration of the electrolytic solution if the electrolysis period is not shorter than a predetermined period (required for the saturation).
When a user specifies the concentration of the sterilizing solution, for example, the concentration of the electrolytic solution to be supplied into the electrolysis chamber is adjusted to a level corresponding to the specified concentration of the sterilizing solution. As a result, the concentration of the sterilizing solution produced through the electrolysis by the electrode set is automatically controlled at a level corresponding to the concentration of the supplied electrolytic solution. Therefore, if the user is allowed to set the concentration of the sterilizing solution, the residual chlorine concentration of the water can be adjusted at a desired level according to the type of the water container or the application of the water treatment system. Thus, the water treatment system is applicable to various types of water containers.
A high-concentration electrolytic solution such as saturated salt water is preliminarily stored in a tank, and the amount of the high-concentration electrolytic solution supplied into the first electrolysis chamber from the tank and the amount of a diluent (e.g., tap water) employed for dilution of the high-concentration electrolytic solution are controlled so as to adjust the concentration of the electrolytic solution in the first electrolysis chamber to a specified level.
The system further comprises a flow path for introducing the to-be-sterilized water into the first electrolysis chamber from the water container, whereby the water is supplied from the water container through the flow path to the high-concentration electrolytic solution supplied into the first electrolysis chamber from the tank so that the high-concentration electrolytic solution retained in the electrolysis chamber is diluted with the water. Thus, the concentration of the electrolytic solution can be adjusted to the specified level.
The concentration of the sterilizing solution produced in the electrolysis chamber is controlled by adjusting the quantity of electricity supplied to the electrode set, i.e., the level of an electric current (charge amount) applied for the electrolysis.
By detecting the level of the electric current flowing through the electrode set, utilization efficiency at which an electrolyte in the electrolytic solution is utilized by the electrode set can accurately be judged. More specifically, where a constant DC voltage is applied between the electrodes, the level of the electric current flowing between the electrodes generally increases as the concentration of the electrolytic solution supplied into the electrolysis chamber is increased, as shown in FIG. 2(a). On the other hand, the amount of the electrolyte (salt) consumed by the electrode set increases as the concentration of the electrolytic solution is increased, as shown in FIG. 2(b). However, the consumption of the electrolyte starts decreasing at a certain concentration level of the electrolytic solution. Therefore, an experiment is preliminarily performed to obtain data to confirm these relationships and, on the basis of the level of the electric current flowing through the electrode set, the concentration of the electrolytic solution is determined which ensures the highest utilization efficiency of the electrolyte in the electrolysis and maximizes the concentration of the sterilizing solution.
Thus, an increase in the NaCl concentration of the water in a swimming pool (water container) can be prevented, which may otherwise occur when the high-concentration electrolytic solution is supplied in excess into the electrolysis chamber and a portion of the electrolytic solution not used for the electrolysis flows into the swimming pool. Therefore, swimmers will not feel uncomfortable in salty water in the swimming pool. Further, an increase in time required for the electrolysis and a reduction in residual chlorine concentration can be prevented, which may otherwise occur due to an excessively low concentration of the electrolytic solution and require a greater amount of the sterilizing solution.
A higher sterilizing effect can also be provided. More specifically, the sterilizing effect of the sterilizing solution is expressed by a product Ct of the sterilizing solution concentration C and a period t during which the sterilizing solution is kept in contact with the to-be-sterilized water.
As compared with a case where the sterilizing solution produced in the first electrolysis chamber is directly supplied into the water container, the Ct value is increased during the passage of the sterilizing solution through the water treatment line where the sterilizing solution produced in the first electrolysis chamber is introduced into the water treatment line at a position upstream of the second electrolysis chamber. Thus, a higher sterilizing effect can be provided. Particularly, where an outlet of the first electrolysis chamber is connected to the second electrolysis chamber, the supplied sterilizing solution can readily be exposed to the atmospheric pressure. Therefore, the construction of the system can be simplified.
A required amount of the sterilizing solution can be supplied as required on the basis of the level of the residual chlorine concentration of the water detected by the residual chlorine concentration sensor.